This study examines the role of the coupling effect between mass and slope, defined as the coordinated variation in particle grain size and topographic slope, in explaining the transition from meandering to braided fluvial systems and elucidates the associated three-dimensional geological responses. In the Lower Triassic of the southern Junggar Basin, a well-developed meandering-braided transition system is documented, with well-exposed sedimentary sections offering insight into the transformation process. Palaeoslope estimation and particle grain analysis confirm the presence of the coupling effect between mass and slope in the study area. This effect is characterised by a general positive correlation between topographic slope and particle grain size and may have contributed to the formation of the meandering-braided fluvial system. Palaeoslope estimation was conducted using Long's (2022) empirically validated formulas, with cross-beds (Hx) and median grain size (Di50) as key input parameters. The vertical sedimentary succession, section stacking patterns and quantitative characterisation of architectural elements from meandering to braided fluvial systems collectively record geological responses during the fluvial pattern transition process.
The Altyn Tagh region preserves extensive Precambrian terranes, but poor exposure and limited high-precision geochronological and isotopic data have hindered reconstruction of its Meso-Neoproterozoic tectonic affinity within Rodinia. This study presents new detrital zircon U-Pb geochronological, in situ Hf isotopic and provenance data from the Mesoproterozoic Taxidaban Group and the Neoproterozoic Suoerkuli Group in the Central Altyn Tagh. The Taxidaban Group is characterised by zircon ages mainly between 1.2 and 1.8 Ga, with a dominant peak ca. 1.4 Ga, and its youngest zircon populations constrain a maximum depositional age of 1150-945 Ma. The Suoerkuli Group shows a broadly similar age spectrum and, together with an age of ca. 930 Ma for volcanic rocks at its base, constrains deposition to approximately 930-896 Ma. Lithological associations suggest deposition in a marine to volcano-sedimentary basin setting. Mesoproterozoic detrital zircons are dominated by positive epsilon Hf(t) values but also include negative values, suggesting a complex source region involving both relatively juvenile crust and reworked older crust. The detrital zircon age spectra and Hf isotopic characteristics differ from those of the Tarim, North China and Yangtze cratons, but are broadly comparable to those of Laurentia, Baltica and Amazonia, supporting possible palaeogeographic affinity with the Laurentia-Baltica-Amazonia system.
The Upper Triassic Yanchang Formation in the southeastern Ordos Basin is a depression-type lacustrine delta system, where strong heterogeneity of delta-front sandbodies hinders hydrocarbon development. We investigated base-level controls on sandbody architecture and developed a quantitative model for tight oil reservoirs. Using core, log, and outcrop data, we established a chronostratigraphic framework of 1.5 long-term and 8 medium-term base-level cycles. The results show systematic sandbody evolution: during early base-level rise, amalgamated multi-storey channel sands developed; during mid-to-late rise, single-storey channel sands interbedded with mudstones formed; at peak rise, thick mudstones with thin sandstones accumulated; during the falling stage, sheet-bar sands developed; and during the rapid fall to early rise, mouth bars were widely distributed. Multiple linear regression (R-2 = 0.398, N = 808, p < 0.001) confirms base-level change as the primary control on sandbody differentiation. We propose a predictive model for sandbody distribution in such delta fronts, providing a robust framework for exploration in the Ordos Basin and analogous basins worldwide.
Ophiolitic chromitites are critical archives of mantle melt transport and ore formation in supra-subduction zone (SSZ) settings, occurring as two distinct ore styles: mantle-hosted podiform and crust-mantle transition zone (CMTZ)-hosted stratiform-like orebodies. However, their genetic linkage remains poorly constrained. The Bursa ophiolite, northwestern Turkey, exposes complementary levels of a single oceanic lithospheric mantle section across the Harmancik and Orhaneli massifs, enabling forearc melt evolution to be traced from deep mantle reaction channels to shallow CMTZ melt-focusing systems. Harmancik comprises fertile lherzolites recording 6%-13% partial melting and refractory harzburgites recording 15%-20% melting, both overprinted by migrating forearc melts and associated with replacive dunite channels and podiform chromitites. In contrast, Orhaneli exposes CMTZ dunite-chromitite assemblages and ultramafic-mafic cumulates, recording shallow melt focusing, magmatic differentiation, and in situ crystal accumulation. These observations suggest that the Bursa chromitites represent a vertically linked ore-forming system in which mantle-hosted podiform chromitites formed in reaction channels, whereas CMTZ-hosted stratiform-like chromitites formed during upward melt focusing, differentiation, fractional crystallisation, cumulus processes, and multistage melt percolation.
Dyke swarms preserve both emplacement geometry and subsequent tectonic overprints, providing valuable constraints on crustal kinematics. Here, we re-evaluate Late Cretaceous tectonic rotation in the Eastern Gangdese belt of the Lhasa terrane, southern Tibet, by applying the net tectonic rotation (NTR) method to published palaeomagnetic and structural data. The preferred solution indicates a 26.2 degrees counterclockwise vertical-axis rotation about a pole at D = 133.7 degrees and I = 38.1 degrees, while restoring the dykes to near-vertical initial orientations. This estimate is slightly larger than previous tilt-corrected results, reflecting the tighter geometric constraints imposed by the NTR framework through the joint restoration of magnetization vectors and dyke orientations. We interpret the observed rotation as the cumulative result of multiple tectonic processes associated with India-Asia convergence, most plausibly including Late Cretaceous Neo-Tethyan oblique convergence and later distributed intracontinental strike-slip deformation. Our results provide a new quantitative constraint on the kinematic evolution of southern Tibet and further demonstrate the value of dyke-based NTR analysis for reconstructing tectonic deformation in structurally complex orogenic systems.
